Thermoplastic components used in automobile production are commonly provided with electrostatically applied surface coatings. For example, thermoplastic parts, such as bumper parts, may be electrostatically painted with an acrylic base and clear coat to give the surface a glossy appearance. In order to promote uniformity of coating for such electrostatically applied surface coatings, it is desirable to enhance the normally low inherent surface electrical conductivity of thermoplastic surfaces before electrostatically coating the surfaces.
It is known to use a solvent-based primer or pretreatment composition containing carbon black in such electrostatic coating operations. This prior art primer composition has not been adapted for use on a production line. Rather, the thermoplastic parts are primed "off-line". The inefficiency inherent in such a coating operation, in an otherwise integrated production system, is apparent.
A solvent-based priming composition, believed to be an quaternary ammonium salt solution in isopropanol, has been used as a surface treatment composition in an "on-line" coating operation. However, this method is attended by some difficulties: isopropanol is quite volatile, making use of solutions in it technically difficult, and thermoplastic surfaces treated with this composition cannot be water-rinsed for environmental reasons.